During the last 20 years, dental implants have become a widely accepted and – in certain parts of the world – a popular therapy in the restoration of partially and completely edentulous patients.Although the general impression of implant therapy is that the success rate is high, infections defined as peri-implant mucositis and peri-implantitis are commonly found. According to available epidemiologic data, it appears that one out of five patients will develop peri-implantitis over time and that peri-implant mucositis is a very common phenomenon among implant patients. As with periodontal diseases, peri-implant diseases are recognised as inflammatory diseases of infectious origin, ultimately leading to loss of bone supporting the implant. Peri-implant mucositis is defined as an inflammatory lesion limited to the surrounding mucosa, whereas peri-implantitis also affects the supporting bone. For practitioners who desire to obtain long-term positive results with implants, risk indicators and possible risk factors for the development of peri-implant infection must be identified.  The early diagnosis of peri-implant diseases and the evaluation of the health status around implants is essential. Most treatment modalities of peri-implant diseases are adapted from those used for the treatment of periodontal diseases; the primary therapeutic approach being aimed at controlling infection. This may involve adjustment of prostheses to allow for proper oral hygiene and professional removal of the biofilm and hard deposits from the implant surface. In advanced peri-implantitis cases a surgical approach may be necessary to gain access to disrupt and remove the biofilm. If appropriate at such a surgical intervention, regenerative treatments to regain the lost bone may also be performed. At present there are limited scientific data on the treatment of peri-implant diseases, and therapeutic interventions in peri-implantitis cases are, in many instances, based on clinical experience. However, research activity in this field is very high, and new data are continuously produced with the expectation of clearer guidelines for the treatment of these conditions in the future.